VTI Instruments Corp.
74
EX1401 Instrument Drivers
Sync
Sync is an event that synchronizes the entire system. The
Sync
interface is used to configure the
synchronization between cards. All cards are simultaneously started by the SYNC signal and then
they synchronize the state machine transition with each other through a coordination signal. The
Line
and
CoordinationLine
properties define which PXI trigger lines and/or Alarms to use to send
these signals.
Start
Once the measurement is initiated by the Initiate command, the instrument completes all preparation
and becomes ready to start taking data immediately. Then the state machine moves to the
Wait for
Start
state. The
Start
interface provides methods and properties to advance to the next state. The
amount of time it takes to reach to
Wait for Start
after measurement
Initiate
command varies
depending on the measurement configuration. For example, it takes longer when the measurement
sample rate (or measurement span) is low because the filter settling time is longer. The
Start
interface is useful when the user wants to have the instrument complete all the preparation and hold
in that state, so that it can start taking data immediately without any delay.
Arm
The instruments must be armed before triggering data acquisition. The
Arm
interface is used to
configure this arming condition. The
Sources
property in the
Arm
interface defines the arming event
sources. The default arming source is
Immediate
, which means automatic arming. The
SourceOperator
property allows the user to define an arming condition by logically combining
multiple arming sources. The
Delay
property defines amount of time the instrument waits before
moving out from
Wait for Arm
state after the defined arming conditions are met. The
ArmCount
property defines how many times the measurement repeats arming and triggering before it
completes. The default is once. Setting
ArmCount
to 0 forces the measurement to repeat arm and
trigger indefinitely until it is aborted by
Abort
command.
Trigger
Data acquisition begins when a triggering condition is met. The triggering condition is configured
using the
Trigger
interface. Similar to Arm interface, the
Sources
property in the
Trigger
interface
define the triggering event sources. Trigger sources can be logically combined using
SourceOperator
in the
Trigger
interface. The
Delay
property defines the amount of time between
the trigger event and the beginning of the data acquisition. The
Delay
value can be negative
indicating pre-trigger data acquisition. In this case, the acquired data block starts earlier than the
trigger event. This is achieved by buffering the data in the instrument’s FIFO prior to the trigger
event. For more information, see the Data Acquisition section.
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